Cognitive Aspects of Human Olfaction: the "What" and "Where" subsystems Evidence from vision and audition suggests cortical processing of sensory information occurs along two anatomically dissociable streams. In the simplest form, these consist of a ventral stream that processes object identification, and a dorsal stream that processes object location. This concept relates to a major question on brain organization, namely, does the brain employ convergent or divergent mechanisms in processing information. Current evidence points to convergence in that spatial information from both vision and audition converges in dorsal regions, and stimulus identity information converges in ventral regions. Here this theoretical framework is tested using olfaction. This is accomplished through 3 specific aims: Aim 1 is a test of the hypothesis that humans can use information obtained through smell to create a spatial map. This is achieved by asking if humans can perform scent tracking, and by examining the effects of odor properties (e.g., identity) and sampling strategies (sniffing frequency) on this behavior. Aim 2 is a test of the hypothesis that humans can localize an odor source without moving their head. This is achieved by asking if humans can perform egocentric olfactory localization and by examining the effects of practice, odor properties (e.g., identity) and sampling strategies (sniffing frequency) on this behavior. Aim 3 consists of using fMRI to probe the neural mechanisms subserving spatial localization of odors. Pilot data from Aims 1 and 2 suggests humans do have some spatial abilities in olfaction. In Aim 3 functional imaging is used to test whether this spatial information is incorporated within previously identified cortical pathways (the dorsal "where" stream). These three aims, which include psychophysics in the field, psychophysics in the lab, and fMRI, combine to form the first comprehensive study of spatial abilities in human olfaction. Results promise to further our understanding of fundamental concepts in brain organization.